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Abstract Plant chloroplasts conduct photosynthesis to convert solar energy into sugars for the carbon source essential for cell living and growth during the day. One fraction of photosynthetic products is stored in chloroplasts by forming starch granules to continue the provision of carbon energy during the night. Currently, profiling the starch temporal pattern requires either: (i) sacrificing the leaves, or (ii) generating transgenic plants at the risk of changing the metabolisms by incorporating a genetically modified granule-bound starch synthase (GBSS). In this paper, we demonstrated a nondestructive method using two-photon fluorescence (TPF) and second-harmonic generation (SHG) imaging to quantify starch granules within chloroplasts of fresh intact leaves across a day-night cycle. We did so using two Arabidopsis lines having normal and excess starch contents: wild-type (Columbia-0) and starch excess 1 (sex1). The starch granules were visualized by SHG imaging, while the chloroplasts in mesophyll cells were visualized by TPF imaging. Our results provided micron scale spatial resolution of starch distribution within leaves and showed starch circadian patterns consistent with those profiled by enzymatic assays in previous studies. We demonstrated that TPF-SHG imaging is a potential tool for revealing the real-time heterogeneity of starch circadian rhythm in leaf cells, without the need for destructive sample preparation.

The sensitiveness of second-harmonic generation (SHG) signal to crystal lattice orientation and crystal symmetry makes it a powerful tool for structural characterization of low dimensional transition metal dichalcogenide (TMD) materials. In this paper, we report the strain-induced SHG enhancement at the edge of the monolayer MoS2 flakes. By performing raster mapping of SHG intensity, the images show an enhanced SHG intensity at the flake edge with cubic-power dependence. The AFM analysis of the MoS2 flake edge with enhanced SHG, indeed, detected a topographic height change as compared to the center region. Micro-Raman spectroscopy analysis shows a blue shift in A1g phonon mode at the flake edge. This edge-enhanced SHG may be attributed to the intrinsic strain effect induced during the chemical vapor deposition growth condition, which modulates the nonlinear susceptibility. The micro-Raman spectroscopy implies that the flake edge has a compressed and stiffened structure in an out-of-plane direction. This work brings out the awareness of the residual strain effect on 2D TMD device performance, and the adequate characterization of the strained structure by SHG intensity mapping.

In this paper, we have demonstrated birefringence modification in regenerated grating in polarization maintaining fiber (RGPMF) by using a CO2 laser annealing technique. After conducting an isothermal annealing procedure followed by a slow cooling process, the birefringence of the RGPMF has been increased. This phenomenon can be explained by the changes in the thermal expansion coefficient and glass transition temperature of the stress applying part at different cooling rates. This process was reversible by reannealing with a subsequent fast cooling process. In our observation, the birefringence exponentially increases with a decreasing cooling rate. The highest and lowest records in the birefringence throughout the annealing process are 4.72 × 10-4 and 3.46 × 10-4, respectively (a difference of 1.26 × 10-4). This finding is useful for the study of the birefringence modification, measurement range, sensitivity, and accuracy of PMF or PMF-related devices.

Optical fibers have been involved in the area of sensing applications for more than four decades. Moreover, interferometric optical fiber sensors have attracted broad interest for their prospective applications in sensing temperature, refractive index, strain measurement, pressure, acoustic wave, vibration, magnetic field, and voltage. During this time, numerous types of interferometers have been developed such as Fabry-Perot, Michelson, Mach-Zehnder, Sagnac Fiber, and Common-path interferometers. Fabry-Perot interferometer (FPI) fiber-optic sensors have been extensively investigated for their exceedingly effective, simple fabrication as well as low cost aspects. In this study, a wide variety of FPI sensors are reviewed in terms of fabrication methods, principle of operation and their sensing applications. The chronology of the development of FPI sensors and their implementation in various applications are discussed.